Role of Secondary Flows on Flow Separation Induced by Shock/boundary-layer Interaction in Supersonic Inlets

[摘要] Flow separation in the scramjet air intakes is one of the reasons of failure of theseengines which rely on shock waves to achieve flow compression. The shock wavesinteract with the boundary layers (Shock/ Boundary Layer Interaction or SBLI) on theintake walls inducing adverse pressure gradients causing flow separation.In this experimental study we investigate the role of secondary flows associatedwith the corners of ducted flows and identify the mechanisms by which they affectflow separation induced by a shock wave interacting with the boundary layers developingalong supersonic inlets. The coupling between flow three-dimensionality, shockwaves and secondary flows is in fact a key aspect that limits the performance and controlof supersonic inlets. The study is conducted at the University of Michigan GlassSupersonic Wind Tunnel (GSWT). This facility replicates some of the features of thethree-dimensional (3D) flow-field in a low aspect ratio supersonic inlet. The studyxxiiiuses stereoscopic particle image velocimetry (SPIV) to measure the three-component(3C) velocity field on several orthogonal planes, and thus allows us to identify thelength scales of separation, its locations and statistical properties. Furthermore, thesemeasurements allow us to extract the 3D structure of the underlying vortical features,which are important in determining the overall structure of separated regions and theirdynamics. The measurements and tools developed are used to study flow fields ofthree cases: (1) Moderately strong SBLI (Mach 2.75 with 6◦ deflection), (2) weakSBLI (Mach 2.75 with 4.6◦ deflection) and (3) secondary corner flows in empty channels.In the configuration of the initial work (moderately strong SBLI), the shock wavesystem interacts with the boundary layers on the sidewall and the floor of the duct(inlet), thus generating both a swept-shock and an incident-shock interactions. Furthermore,the swept-shock interaction taking place on the sidewalls interacts with thesecondary flows in the corners of the tunnel, which are prone to separation. Thisinteraction causes major flow separation on the sidewall as fluid is swept from thesidewall. Flow separation on the floor should be expected given the strength of theSBLI (moderately strong case), but it is instead not observed in the mean flow fields.Our hypothesis is that interacting secondary flows are one of the factors responsiblefor the sidewall separation and directing the incoming flow towards the center-planeto stabilize and energize the flow on the center of the duct, thus preventing or at leastreducing, flow separation on the floor.The secondary flows in an empty tunnel are then investigated to study their evolutionand effects on the primary flow field to identify potential separation sites. Theresults from the empty tunnel experiments are then used to predict locations of flowseparations in the moderately strong and weak SBLIs. The predictions were found tobe in agreement with the observations.

[发布机构] University of Michigan

[效力级别] Aerospace Engineering

[关键词] Shock wave Boundary Layer Interaction;Aerospace Engineering;Engineering (General);Science (General);Engineering;Science;Aerospace Engineering